In those silver halide photographic photosensitive materials in which dye donating compounds form or release diffusible dyes by means of a reduction reaction, such as those disclosed, for example, in U.S. Pat. Nos. 4,199,354, 3,980,479, 4,139,379 and 4,783,396, used in methods of image formation involving diffusion transfer-type color photosensitive materials containing dye donating compounds which form or release diffusible dyes, a competitive reaction occurs between the silver halide reduction reaction and the reduction reaction of the compound which has diffusible dye donating properties used for image formation. The minimum density parts are formed by the silver halide and the reducing agent reacting at a higher rate than the reaction between the reducing agent and the diffusible dye donating compound. Consequently, the silver halide emulsion used must have a very high development rate. But development of unexposed silver halide (referred to hereinafter as development fogging) tends to occur readily with a further problem of a fall in color purity.
Furthermore, development fogging is also liable to occur as a result of high temperature processing with thermally developed diffusion transfer color photographic photosensitive materials. In this case, once again, a lowering of color purity is liable to occur. Methods in which development inhibitors are added to thermally developable silver halide photographic photosensitive materials in order to inhibit development fogging are known. Examples include those disclosed, for example, in JP-A-59-168442 (U.S. Pat. No. 4,500,627), JP-A-59-111636 (U.S. Pat. No. 4,614,702), JP-A-59-177550, JP-A-60-168545, JP-A-60-180199, JP-A-60-180563, JP-A-61-53633, JP-A-62-78554, JP-62-123456, JP-A-63-133144 and JP-A-2-44336. (The term "JP-A" as used herein signifies an "unexamined published Japanese patent application".) However, compounds which inhibit development fogging are generally adsorbed on silver halides and so there is competitive adsorption with the sensitizing dyes, which are similarly adsorbed on the silver halide, resulting in an undesirable loss of photographic speed. Known methods for overcoming this problem involve converting the development inhibitor to a precursor (a precursor of the development inhibitor) which is not adsorbed on the silver halide at the time of the exposure and inhibiting development fogging by releasing the inhibitor by the action of heat or alkali during development processing.
However, the release reaction rate is sometimes inadequate with these methods, or the release reaction does not take place efficiently because of side reactions. There also are cases in which the intended inhibition of development fogging does not occur effectively.
On the other hand, there are compounds which are generally known as compounds which release development inhibitors in accordance with the exposure in an imagewise manner. For example, there are the so-called DIR hydroquinones disclosed, for example, in U.S. Pat. Nos. 3,379,529, 3,620,746, 4,377,634 and 4,332,878; JP-A-56-153342, JP-A-49-129536 and JP-A-56-153336. The compounds generally emphasize development which has an effect between layers (the so-called lamination effect) during the development of silver halide photosensitive materials. The compounds are used with a view to improving color reproduction. However, the compounds also give rise to the same problems as the precursors of development fogging inhibitors described above. That is to say, the release of development inhibitor from the oxidized form of the DIR-hydroquinone is not rapid and does not occur efficiently. Thus it is impossible to realize a high efficiency. For this reason, there is a demand for a method by which development inhibitor is released at a satisfactory rate and with good efficiency in a heat developable silver halide photosensitive material.
A method for the fast and efficient release of development inhibitor has been disclosed in JP-A-59-198453, but its effect in diffusion transfer-type silver halide color photosensitive materials or heat developable diffusion transfer-type silver halide color photosensitive materials which contain dye donating compounds which form or release dyes by reduction is unknown.
Furthermore, it is difficult to increase the concentration of base to an extent that provides a satisfactory release rate in heat developable silver halide photosensitive materials in a method in which a base is produced during the development of the photosensitive material, without supplying base to the reaction. Hence, a method which provides a satisfactory release rate and release efficiency even with a low base concentration is especially desirable for obtaining good color reproduction.
It is impossible to improve color reproduction satisfactorily in diffusion transfer-type silver halide color photosensitive materials, especially diffusion transfer-type silver halide color photosensitive materials which contain dye donating compounds which form or release diffusible dyes as a result of reduction because emulsions which fog easily are often used. The present invention is intended to overcome the problems outlined above and provide diffusion transfer-type silver halide color photographic photosensitive materials which have good color reproduction.